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Leaf lenses: a finer focus.

Leaf lenses: A finer focus

Cellular "lenses" on the leaves of some plants allow them to regulate the amount of sunlight reaching their photosynthesis centers, according to two studies described last week.

Raymon A. Donahue and his co-workers at the University of Wyoming in Laramie used scanning electron microscopy and fiber-optic light detectors to track light paths within leaves of the Rocky Mountain weed Thermopsis montana in sun and shade. They found that the leaves' transparent, outermost cells become significantly more convex in the shade, thus capturing diffuse light from a broader range of angles and focusing it within a particular, light-sensitive region of the energy-converting machinery within the leaves. From these observations and from metabolic measurements made with a portable gas-exchange system, the researchers conclude that "T. montana cells are optically specialized to enhance whole leaf photosynthesis in specific light environments." They presented their findings in Snowbird, Utah, at the annual meeting of the Ecological Society of America.

Biologists have indirect evidence for similar lens effects in more than 40 plant species, adds Wyoming's Greg Martin. But researchers have had difficulty measuring the energy benefits of the lens system. In a study he described at the meeting, Martin used dental latex to make fine-resolution molds of leaf surfaces kept in sun or shade. He then used the molds to create leaf-surface replicas made of agarose gel. From measurements of the refractive properties of these replicas, he concludes that some shaded leaves, compared with sun-drenched leaves, can intensify captured light up to 26 times. He also notes that in intense sun, some plants' leaf surfaces seem to focus light onto a cell layer that absorbs potentially damaging energy excesses.
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Title Annotation:regulation of photosynthesis
Publication:Science News
Date:Aug 11, 1990
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